Manchester Memoirs, Vol. lix. (191 5), No. i>. 



IX. On two cases of Parallelism in the Aphidae. 



By A. W. Rymer Roberts, M.A. 



(Received and read March 23rd, 19/5.) 



The existence of parallel races of insects, having a 

 common ancestry, but differing in their habits, and some- 

 times also in their external morphology, was brought into 

 prominence by Blochmann, Dreyfus and Cholodkovsky (I) 

 in the course of their early researches into the biology of the 

 Chermesince, especially Chermes abietis and Oh. strobilobins. 

 Since that time — the closing years of the last century — a 

 doubt has arisen as to whether the races of Chermes which 

 were then considered as forming the most prominent 

 examples of the phenomenon, the moncecious and 

 dioecious forms, ought properly to be regarded as parallel 

 races, rather than as biological species which have evolved 

 and are maintaining a different life-history. Cholodkov- 

 sky (2) has more recently given different specific names 

 to the moncecious and dioecious forms, maintaining that 

 they are distinct biological species, though corresponding 

 stages are morphologically almost indistinguishable. But 

 he has been obliged to admit, in conformity with the 

 researches of Bonier (3), that although in the forests of 

 Russia the moncecious forms constitute different biological 

 species, yet in Switzerland, where he has also made 

 experiments, both moncecious and dioecious forms may 

 arise from the same stem-mother. This he interprets as 

 the primitive condition, while the separation of the two 

 forms in Russia, he regards as the initial stages in the 

 further evolutionary development of separate species. As 



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